Go forward for a bit and you'll need to drop to a lower level. Either smash your way through the fences or peacefully use the ramp. Turn left after a while, and then right (1/4). After driving on a bit of dirt, you'll enter a tunnel. Keep going all the way through the highway and you'll reach the checkpoint easily (2/4). Follow the highway for some more time, and when you're on the Western part, enter the left lane. Follow the road that the arrows point to and turn left when you reach the shop (3/4). Turn right and turn right again after a while. You'll encounter 3 ramps that will take you to the upper level (4/4). Keep going and turn left to end up where you started.